1. Field of the Invention
The field of the invention is compressible offset printing blankets, that is, blankets which are compressible in use and which are particularly suited for use in offset printing. Such blankets must be so constructed as to undergo repeated compression and rapid recovery during printing and have a long life so that long runs without shutdown are possible.
2. Description of the Prior Art
Conventional offset printing blankets are now made with a multi-ply fabric base and a vulcanized elastomeric face. Compressible blankets consist of a multi-ply fabric base with a cellular compressible layer or layers buried somewhere in the base and a vulcanized elastomeric face. The majority of such compressible blankets comprise a single compressible layer, but some are made with two compressible layers. The compressible layer may be a spongy elastomeric material deposited from a cement of an elastomeric polymer which is made spongy in various ways, as by beating air into the cement, laying down a layer of the frothed or foamy cement on the fabric carcass which may already have been vulcanized, followed by removal of the volatile organic solvent content of the cement, and completion of the blanket, as by application of a woven fabric sheet followed by laying down a solid elastomeric facing layer made from a rubbery polymer capable of withstanding the solvent action of the ink used in the printing process and by vulcanization of the unvulcanized elastomeric components of the blanket in a conventional vulcanizing unit.
Another way of obtaining the compressible layer is described in U.S. Pat. No. 3,147,698 issued in the name of William C. Ross and assigned to W. R. Grace & Co. This patent is directed to making the compressible material by impregnating a highly porous felted fibrous web with an elastomeric material in solution or water dispersion, typically natural rubber latex, followed by vulcanization, to produce a sheet having certain specific characteristics of firmness and porosity.